The present invention relates to an information recording apparatus provided with a magnetic head and a magnetic disk; and, more particularly, the invention relates to a magnetic disk drive whose track density is significantly improved.
A magnetic disk drive positions its head by use of a rotary actuator on a magnetic disk rotated by a spindle motor, thereby recording/reproducing information magnetically from/on many tracks formed on the magnetic disk concentrically. In order to follow a target data track, it is required to precisely measure the relative position between each head and the magnetic disk, thereby reducing any misalignment caused by a difference in thermal expansion, as well as the influence of such disturbances as the vibration of the spindle motor and the vibration rotary actuator during rotation. The information which indicates the relative position between the head and the magnetic disk is provided in the form of a head position signal. It is essential to produce this head position signal as accurately as possible so as to improve the track density. To achieve this object, there is a technique employed widely, as disclosed in Japanese Patent Prepublication No. 58-222468. The technique obtains the head position signal from each shipment pattern written on the magnetic disk before the delivery of the magnetic disk drive. The special pattern is referred to as a servo pattern.
FIGS. 13A to 13D show how a servo pattern is formed up in a servo area 31 with use of a servo track writer. The servo track writer, as disclosed, for example, in Japanese Patent Prepublication No. 64-48276, is used to write tracks at equal pitches on a magnetic disk. In this case, a description will be given of a conventional technique that has been employed widely; wherein, one track is divided into two so as to write a servo pattern therein respectively.
How servo patterns are written in three consecutive tracks on the magnetic disk sequentially is shown in FIGS. 13A, 13B, 13C, and 13D. Usually, because the core width of the write element of the magnetic head is wider than a half of a track, a servo pattern becomes wider than the target track just after the pattern writing. For example, the width of the servo pattern newly written in track 16-2 in FIG. 13A is wider than the width of the servo pattern written in the track 16-1. Following this process, a servo pattern written at the previous rotation of the magnetic disk is erased at one side before another servo pattern is written as shown in FIGS. 13B and 13C.
Then, as shown in FIG. 14A, after the magnetic disk is rotated several times, four patterns from A burst 43-1 to D burst 43-4 are formed into the same width as that of one track. An ISG part 40 and an AM (Address Mark) part 41 are formed as consecutive patterns in the track width direction. When a servo pattern is written actually, it needs a time for moving the head only by a half of the track pitch in the track width direction. In the case of a method of rotating the magnetic disk idly once between the states in the charts 13A and 13B, 13B and 13C, and 13C and 13D, respectively, servo patterns are written in the servo areas of one track while the magnetic disk is rotated twice.
FIGS. 14B and 14C show how a head position signal is generated from a servo pattern formed in the servo area 31. In the pattern shown in FIG. 14A, the ISG part 40 is a continuous pattern formed so as to reduce the influence of the magnetic irregularities of the medium or the fluctuation of the flying height of the magnetic disk. A servo decoder block activates an auto gain control (AGC) so as to reproduce the ISG part 40. The AGC is turned off when the AM part 41 is detected, thereby providing a function for normalizing the following reproduced width of the following burst part 43 at an amplitude of the ISG part 40. A Gray code part 42 describes the track number of each track 16 with a Gray code. In this part there is often described sector number information, as well. The burst part 43 is formed as a checker-like pattern so as to obtain accurate information on the target position in the radial direction of the magnetic disk. It is necessary for the head to follow the center of each track accurately. This pattern is formed so that the center between A burst 43-1 and B burst 43-2 or between C burst 43-3 and D burst 43-4 is aligned with the center of each track 16. A pad part 44 is formed so as to absorb the delay of the decoder block system so that clock generation is maintained, while the servo decoder block reproduces the servo area 31.
The head 11 provided with a read element reproduces servo patterns while running on the position A from left to right as shown in FIG. 14A. FIG. 14B shows an example of the reproduced waveform at this time. The reproduced waveforms of the AM part 41, the Gray code part 42, and the pad part 44 are omitted here so as to simplify the description. The servo decoder block detects the amplitudes of the four bursts from A burst 43-1 to D burst 43-4. The amplitude of each burst is converted to a digital value by an A/D converter and transferred to a CPU. The CPU calculates the difference between amplitudes of the A burst 43-1 and the B burst 43-2, thereby calculating a position signal N. In FIGS. 14A-14C, expressions are also shown. Each expression normalizes such a difference between amplitudes with the ISG amplitude.
To provide this function of normalization, the servo decoder block controls the AGC so as to fix the amplitude of the ISG 40. In the same way, the Q position signal is calculated from the difference of amplitude between the C burst 43-3 and the D burst 43-4.
FIG. 14C shows a head position signal generated as described above. The position signal N becomes 0 at position B where the center of the head is positioned at equal distances to both the A burst 43-1 and the B burst 43-2. The N position signal is switched between positive and negative in proportion to the misalignment distance from this center position. For example, the position signal N is obtained from the reproduced waveform of the position C shown in FIG. 14A at the position C shown in FIG. 14C. The CPU compares the absolute value of the position signal N with the absolute value of the position signal Q, thereby inverting the positive/negative states of those position signals N and Q and linking them so as to generate continuous position signals, respectively. In many servo patterns, the position where the position signal N becomes 0 is set as a following center, thereby controlling the voice coil motor for driving the head. If there is no misalignment between the write element and the read element in the track width direction, the edge of each of A burst 43-1 and B burst 43-2 is aligned to the center of each track 16.
The use of the above conventional technique can therefore reduce the misalignment caused by the difference in thermal expansion, as well as the influence of such disturbance as the vibration of the spindle motor and the rotary actuator during rotation. Consequently, the accuracy of following each target data track can be improved, thereby further improving the track density.
However, the above conventional technique has an inherent a problem; that is, when a servo area is written with use of a servo track writer, the vibration of the servo track writer is fixed on the magnetic disk as a difference in position between servo patterns in servo areas. In particular, because the non-repeatable run-out that does not depend on the rotational position of the disk adds up error components that are different among tracks, there is no effective method for removing the non-repeatable run-out. Because a servo area, once it is formed, cannot be rewritten after the shipment of the magnetic disk drive, the head comes to follow servo patterns in each of which error components are added up. According to a technique disclosed in Japanese Patent Prepublication No. 9-35225, it is possible to effectively compensate such error components of the position signal, which is synchronized with the rotation of the object disk. However, the technique still has other problems; for example, a productivity problem occurs in that a long time is needed to create compensatory data and write the data, and an efficiency problem occurs in that formatting of the drive is not done so efficiently, since a second data area is necessary for the above compensatory data in this case.
There is also another problem in that the end of a written servo area is not aligned to the start of another servo area written during the previous rotation of the disk. This problem is caused by the non-repeatable run-out of the servo track writer.
FIG. 8A shows the position signal of N decoded from a servo area consisting of sectors 1 to 72, which is equivalent to one round of the magnetic disk. The vertical axis in FIG. 8A denotes hexadecimal data fetched by the CPU, which is proportional to a distance. The center of each track is set to 0x5000.
FIG. 8A shows an example of the writing of a servo pattern in a servo area, started at sector 1, so as to simplify the description. A space between sectors 72 and 1 in the center part in FIG. 8A is a discontinued portion where the above misalignment occurs. When a servo area is written, such a discontinued portion is always formed once per revolution of the disk, thereby a discontinuity is generated in the decoded head position signal. Just after such a discontinuity in this position signal, an error position signal, which denotes a difference between a target position signal and an observed position signal, becomes large, making it difficult to control the head accurately in the radial direction. When the accuracy of head positioning is degraded, an interference occurs between a target track data area and an adjacent track data area, whereby the error rate is poor/inferior. Accordingly, the reliability of the magnetic disk drive is lowered. This is also a problem arising from the conventional technique.
According to a technique disclosed in Japanese Patent Prepublication No. 9-259554, a servo signal is written so as to compensate a misalignment on the object magnetic disk, whereby it can be expected to effectively compress error components of a position signal. In this case, however, because there is no compensatory device used for written servo areas, it cannot remove error components caused by the vibration component peculiar to the write head of the servo track writer and the uneven surface of the magnetic disk. This is also a problem that has not been solved by the above conventional technique. In this specification, this discontinued portion generated between the start of a written servo area and the end of another written servo area (i.e. discontinued point formed once per round at an index) will be referred to as a knot in a servo pattern.
In addition, each of many magnetic disk drives are provided with a function to stop the write operation if the head goes far out of a target track due to an external shock, or the like during a write operation. This is to prevent adjacent tracks from overwriting. This function makes it possible to use a method employed widely for stopping a write operation on the basis of a decision that an external shock has been applied to the object disk if an error position signal, which denotes a difference between a target position signal and an observed position signal, becomes larger than a predetermined threshold. However, because such an error position signal adds up various error factors caused by the servo track writer, the signal cannot satisfy a required accuracy of detection as a reference signal to stop the write operation. In particular, because the error position signal has a large value at a knot in a servo pattern, the write operation is stopped even during a normal following operation in which no external shock is applied to the disk. Accordingly, the performance of the magnetic disk drive in such a write operation is lowered. This has also been a problem arising from the above conventional technique.
This is why a new technique has been sought to improve the accuracy in positioning by compensating the error in servo areas, caused by the non-repeatable run-out of the servo track writer in a magnetic disk drive that decodes the head position signal from each of those servo areas, thereby improving the data track density, preventing adjacent tracks from fatal errors of overwriting, and improving the reliability of the magnetic disk drive. Under such circumstances, it is an object of the present invention to provide a magnetic disk drive that can meet these requirements.
In order to achieve the above object, the magnetic disk drive of the present invention forms one of a plurality of servo areas as a servo area having more burst parts than other servo areas on the object magnetic disk. The number of such burst parts is expressed in, for example, a servo address mark. In addition, a plurality of such burst parts are separated from each another by a pattern different from the address mark or by a gap, thereby making it easier to detect each burst part.
A servo track writer used to write servo areas on each magnetic disk in the magnetic disk drive starts writing in a servo area having more burst parts than other servo areas during the first rotation of the disk, and maintains the writing by appending in some burst parts in the servo area having more burst parts than other servo areas at the second rotation of the disk. When decoding the head position signal from the servo area having more burst parts than other servo areas, an averaging processing is executed for the head position signals decoded from the burst parts written at the first rotation of the disk and decoded from the burst parts at the second rotation of the disk. At this time, it is preferable to vary the weighing coefficient of the averaging processing in each servo area.
Concretely, the magnetic disk drive of the present invention is provided with a magnetic disk having a plurality of servo areas and a servo decoder block for decoding the head position signal from those servo areas. The magnetic disk drive of the present invention is characterized in that one of those servo areas is formed so as to have more burst parts than other servo areas. The servo area having more burst parts than other servo areas includes a burst part (n+1) written by the servo track writer at the n-th rotation of the disk (n: a positive integer) and a burst part written at the (n+1)th rotation.
The burst part in the servo area having more burst parts than other servo areas can be divided into a plurality of groups separated with a pattern or a gap therebetween, respectively. A pattern for separating a burst part into a plurality of groups can be a pattern different from a servo address mark.
A servo area can be formed so as to have a servo address mark whose pattern is varied according to the number of included burst parts.
The number of servo areas having more burst parts than other servo areas respectively should preferably be a number obtained by subtracting one from a multiplier of 2.
The servo decoder block, after decoding the head position signals from a servo area including more burst parts than other servo areas, averages a plurality of position signals decoded from those burst parts. In this averaging processing, it is preferable to vary the weighing coefficient of the averaging processing for a plurality of position signals in each servo area, thereby connecting those head position signals smoothly at the knot in the servo pattern.
The magnetic disk drive of the present invention has a plurality of data areas formed separately in a plurality of tracks in the radial direction and a plurality of servo areas formed separately in the circumferential direction. The magnetic disk drive also has a servo decoder block for decoding the head position signal from each of the servo areas. Each of those separated servo areas is formed by combining the first servo area with the second servo area having more burst parts than the first servo area.
Furthermore, the magnetic disk drive of the present invention is provided with a magnetic disk having a plurality of servo areas separated by a plurality of data areas respectively in the circumferential direction and a servo decoder block for decoding the head position signal from each of those servo areas. In the magnetic disk drive, each of a plurality of servo areas has a burst part and one of those servo areas has duplicated burst parts.
The magnetic disk drive of the present invention is provided with a magnetic disk having a plurality of servo areas separated by a plurality of data areas respectively in the circumferential direction and a servo decoder block for decoding the head position signal from each of those servo areas, and each of those servo areas has a burst part and one of those servo areas has another burst part in addition to the above burst part.
The magnetic disk drive of the present invention also has a plurality of data areas formed in a plurality of tracks in the radial direction and a plurality of servo areas formed in the circumferential direction of the magnetic disk respectively and a servo decoder block for decoding the head position signal from each of those servo areas. In the magnetic disk drive, the servo decoder block is provided with a function for connecting the head position signals smoothly at each knot in the servo pattern. The knot appears once per rotation of the disk when the servo track writer writes servo areas on the disk.
Furthermore, the magnetic disk drive of the present invention is provided with a head having a write element and a read element, a magnetic disk having a plurality of servo areas including a burst pattern respectively for generating a signal depending on the positional relationship between each of the tracks formed concentrically and the head, and a servo decoder block for generating a signal representing the positional relationship between each of the tracks and the head according to a reproduced signal from the burst pattern through the head. In the magnetic disk drive, the servo areas are divided into a plurality of types, in each of which the number of burst patterns is varied from others in the circumferential direction.
The magnetic disk drive of the present invention is also provided with a head having a write element and a read element, a magnetic disk with a plurality of servo areas including a burst pattern for locating the center of each of a plurality of concentric tracks, and a servo decoder block for generating a signal representing the positional relationship between the center of each track and the head according to the reproduced signal for each burst pattern through the head. In the magnetic disk drive, the servo areas are divided into a plurality of types, in each of which the number of burst patterns is varied from others in the circumferential direction.
The above servo areas can be divided into two types; one type having one set of burst patterns written in the circumferential direction and the other type having two sets of burst patterns written in the circumferential direction. Each burst pattern determines the center of each track. Servo areas having more burst patterns in the circumferential direction respectively than other servo areas can exist adjacent to each another.
According to the present invention, therefore, it is possible to improve a reliability of the magnetic disk drive and the track density, since the highly continuous head position signal is followed, thereby improving the accuracy of adjacent track pitches. In addition, it is possible to obtain a high reliability for the magnetic disk drive and improve the access performance of the magnetic disk drive, since misdetection in each discontinuous point of the head position signal is reduced when an external shock is detected with use of the head position signal.